Why do Stars Twinkle?

As the stars shine away in the night, I often sit by the window to have a glimpse of the sky above us. Let alone the telescopes and binoculars, the tiny little stars that twinkle in the sky above us are a delight for the eyes. The night sky looks as if a large canvas has been splashed with royal blue and dotted with serene white spots that twinkle and sparkle to light up the entire sky.

The twinkling of the stars is actually a scientific phenomenon, which is known as stellar scintillation or astronomical scintillation. Scintillation is a generic term used to describe the rapid variations in apparent brightness or color of a distant luminous object, when viewed through the atmosphere of the

Earth. Wind motion, turbulent air, and varying temperature scales in the atmosphere, are some of the major factors that play a role in the refraction of light rays.

To understand this phenomenon, you should first know some basic concepts in astronomy. The stars emit light in the form of light rays. They are visible to us because of the fact that these light rays travel through several layers of atmosphere that surrounds the Earth. Earth's atmosphere is made up of several layers of gases that vary in their density.

Thus, when the light rays emitted by the stars travels through the atmosphere, they undergo refraction, i.e., they are bent. The degree of refraction depends on the density of the atmosphere. Owing to several layers of different densities, the rays of light emitted are randomly refracted several times, in random directions. This leads to the effect of "twinkling", which is merely an interpretation of refracted light by our eyes.

The effect of the phenomenon of astronomical scintillation is always more pronounced near the horizon than near the zenith.

This is the reason why the stars that are closer to the horizon seem to twinkle more, because they have to pass through a larger distance of atmosphere. Thus, the farthest ones seem to exhibit the maximum twinkling, due to excessive refraction of the light rays.

In case you are curious about why the planets do not usually twinkle, then you must know that planets are relatively closer to the Earth. Thus, the twinkling is not noticeable, owing to the smaller distance, which leaves little or no room for visible refraction.